Principal lymphoid organs of the body. Embedded in connective tissue and clustered along lymphatic vessels.

Where do Aggregations of Lymph nodes occur?

Near the body surface in inguinal, axillary, and cervical regions of the body.

What are the two basic functions of Lymph nodes?

Filtration and immune system activation.

What is Filtration?

Macrophages destroy microorganisms and debris.

What is Immune System Activation?

Monitor for antigens and mount an attack against them.

What is the structure of a Lymph Node?

Bean shaped and surrounded by a fibrous capsule.

What are the distinct histologically regions of Lymph Nodes?

Cortex and a medulla.

What is the circulation in the Lymph Nodes?

Only lymph nodes filter lymph. Lymph enters via afferent lymphatic vessels. It meanders through these sinuses and exits the node at the hilus via efferent vessels. Because there are fewer efferent vessels, lymph stagnates somewhat in the node. This allows lymphocytes and macrophages time to carry out protective functions.

What is the Spleen?

Largest lymphoid organ, located on the left side of the abdominal cavity beneath the diaphragm. It is served by the splenic artery and vein, which enter and exit at the hilus.

What are the functions of the Spleen?

Site of lymphocyte proliferation, immune surveillance and response, cleanses the blood. Stores breakdown products of RBC's for later reuse. Stores blood platelets. Site of fetal erythrocyte production.

Remaining splenic tissue concerned with disposing of worn out RBC's and bloodborne pathogens.

What is the Thymus?

A Bilobed organ that secretes hormones (thymosin and thymopoietin) that cause T lymphocytes to become immunocompetent.

How does the size of the Thymus vary with age?

In infants it is found in the inferior neck and extends into the mediastinum where it partially overlies the heart. It increases in size and is most active during childhood. It stops growing during adolescence and then gradually atrophies.

How does the Thymus differ from other lymhoid organs?

It functions strictly in T lymphocyte maturation, it does not directly fight antigens.

What do the hormones of the Thymus do?

Stimulate lymphocytes to become immunocompetent.

What are the Tonsils?

Simplest lymhoid organs; form a ring of lymphatic tissue around the pharynx.

What are Palatine Tonsils?

Either side of the posterior end of the oral cavity.

What are the Lingual Tonsils?

Lie at the base of the tongue.

What are the Pharyngeal Tonsils?

(Adenoids) - posterior wall of nasopharynx.

What are the Tubal Tonsils?

Surround the openings of the auditory tubes into the pharynx.

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